Electric-current-controlling device.



L. BRADLEY.

ELECTRIC CURRENT CONTROLLING DEVICE. APPLICATION FILED JAN. 29. 1912.

1,120,018. Patented Dec. 8,1914.

, Q N 8 n-ue-mtoz l Wane ooze LYNDE BRADLEY, 0F MILWAUKEE, WISCONSIN.

ELECTRIC-CURRENT-CONTROLLING DEVICE.

Specification of Letters Patent.

Patented Dec. 8, 1914.

Application filed January 29, 1912. Serial No. 674,105.

To all whom it may concern:

Be it known that I, LYNDE BRADLEY, a citizen of the United States, residing at Milwaukee, county of Milwaukee, and State 5 of Vtis'consin, have invented new and useful Improvements in Electric-Current-Controlling Devices, of which the following is a specification.

My invention relates to improvements 1H electric current controlling devices of that type in which a compressible resistance medium or member is employed, and variations produced in the electric current by varying the pressure upon such resistance medium or member.

crate satisfactorily for varying the current desired to maintain the current without variations in a circuit which includes such a resistance medium or member, a difiiculty has been experienced owing to changes in the temperature. After the compression has been brought to the desired degree, if the ance column of this type, the temperature will continue to increase for a considerable period of time, and where the column is composed of a series of carbon disks, the resistance of the column diminishes with the increase in temperature. With other materials composing the column, a temperature increase might be effective to increase the resistance, but in either case the volume of the current is subject to an uncontrolled variation, and this requires a readjlistment of the means for mechanical compression if a current of substantially constant volume and pressure is to be maintained in the circuit.

The object of my invention is to provide means for automatically changing the mechanical pressure upon the resistance medium or member in such proportion to its variation in temperature as to maintain a substantially uniform resistance regardless of temperature changes.

In the drawings Figure 1 illustrates, in elevation, a series of resistance columns of the described type with my invention embodied therein, one of said columns being shown in central Vertical section. Fig. 2 is a detail view of a set of connections which may be employed in case the resistance of the column increases with increased temperature.

Devices of the above mentioned type opcurrent continues to pass through a resist- Like parts are identified by the same reference numerals throughout both views.

A set of resistance columns 1 are each provided at one end with a cap member 2 and compressed by a compression bar 3. In the specific construction illustrated, the columns 1 are arranged in pairs and the columns of each pair are actuated from the compressionbar 3 through an equalizing bar at. A cap member 5 is mounted upon the opposite end of each column and the columns are lifted until the cap members 5 engage stops 6, after which a continued inward movement of the compression bar 3 compresses the columns 1. It is not material to the invention herein claimed what means are employed for actuating the compression bar It may be assumed, however, that this bar is lifted by a rod 10, which preferably has a foot piece 11 at its lower end between which and the compression bar 3, a set of springs 12 are mounted, whereby an upward pull upon the r0d10 will impart a resilient upward pressure to the bar 3. The general object of these springs is well known in the art, their function being to hold the carbon disks in contact with each other during all current controlling periods, and to secure gradations in pressure, which would not be possible if the otherwise rigid compressing members were not cushioned. The lower spring operates more expansively and under lighter pressures than the upper one, the latter being compressed when the shoulder formed by the hub on foot piece 11 contacts with it. All of the parts above described may be of any ordinary construction, except as hereinafter explained.

For the purpose of my present invention, I provide fixed abutments 15, one for each resistance column. Rods 16 extend from these abutments 15 (preferably through apertures in the central portions of the columns 1) and the stops 6 are mounted upon the unconnected end portions of these rods. Beyond these stops, the unconnected ends of the rods pass through guides 17.

The rods 16 are electrically insulated from the material composing the columns 1. They are formed of a material which expands when heated, and since the rods are exposed to the heat generated by the electrical current in the columns, it is obvious that as the heat increases, the rods will lengthen. The extent to which the rods will lengthen with each added degree of heat depends upon the character of the material employed, but by using proper alloys, it is possible to provide rods which will expand and reduce the pressure upon columns of carbon disks-in such'proportion to the increased heat that the resistance of said columns will remain substantially constant. It will be understood that the decrease in electrical resistance due to heat will thus be compensated by an increased electrical 'resistance due to a reduction in pressure. Exact compensation would of course not be possible ifno expansible cushion were employed, for the reason that the carbon disks are substantially inelastic, and a very slight variation in the length of the tube would relieve the disks from all pressure and al- .low themto separate.

ance oi the units so that instead of securing Such a. reduction in pressure would greatly increase the resista zero temperature co-etficient, the units would havea positive temperature co-eflicient substituted for the negative tempera-.

ture coeflicient of the ordinary carbon column, the resistance of which decreases as the temperature increases. By cushioning the compression bar 3 upon the springs 12 and employing a thermally expansible member or rod 16, whereby the expansion of the rod 16 otl'sets the-decreased resistance, and

the expansion of the spring ofi'sets excessive decreases in pressure (and excessive increases in resistance) which would otherwise result trom such expansion of the rod, it'is obvious that while the column has a negative temperature co-efiicient and each individual unit may be said to have a posime temperature co-etficient due, to the fact that the relatively'fixed abutment. 6 is connected with the rod 16, yet the apparatus as a, whole has a zero temperature co-efiicient due to the presence of the spring in the general combination. v

In Fig. 2.1 have illustrated mechanism for transmitting the movements of the expanding rods toincrease the pressure upon the column. With nearly all, if n'otv all, columns formed of a series of separate disks, a temperature increase decreases the resistance, but if a compressible substance, were employed in a one piece column, conditions might occur in which the resistance would increase with increased temperature. In such cases my invention may still be applied by employing rods 16 which are connected with each other in pairs by links 20 at their otherwise unconnected ends, and these'links may be connected by rods 21 with equalizing bars 4. In such cases the'push of the columns maybe exerted against fixed stops 6 which are therefore not affected in position by the expansion of the rods 16. The pressure of the expanding rods 16 is therefore exerted through the rods 21' to pull use in connection with variable resistance columns, which are included in'the field circuit of an electric motor. It will be understood by those familiar with this art that variable resistance columns used to regulate the delivery of current to the armature of a motor, are usually cut out of circuit when the desired speed is attained, and the speed of the motor is thereafter controlled by varying the resistance in the field circuit. By providing means whereby pressure resistance columns inthe' field circuit may be automatically adjusted to keep the resistance constant notwithstanding temperature changes, I am enabled to adjust the controller for the desired speed immediately after starting the motor and without any necessity for subsequent manual readjustments. But I do not limit the scope of my invention either to a use in connection with 'such field circuits nor to a use in combination with a motor or any part thereof.

Havingthus described my invention, what I claim as new, and desire to secure by Letpressure of the column exerted through the column cap when the latter is pushed against said stop, and a column actuating member at the end of the column opposite said stop.

2. The combination with an apertured compressible resistance medium for controlling electrical circuits, of an apertured cap therefor at each end of said column, a fixed support at one end of the column, a rod expansible under theinfluence of heat, connected at one end to the fixed support and extending through said aperture, a cross pin extending through; said rod and adapted to be engaged by one of the caps, a member longitudinally movable on said rod against the other of said caps', and means for applying pressure to said last mentioned member.

3. An-electrical current controller, comprising a resistance unit including a comthe medium,.said resistance medium having a negative temperature co-efficient, and said resistance unit having a positive temperature co-eflicient converted into a zero temperature co-eflicient by the action of said tension exerting means.

4. An electrical current controller, including the combination of a compressible resistance medium having a negative temperature co-efficient, and the resistance of which is diminished with increasing pressure, means for applying pressure to said resistance medium, and heat controlled means for automatically reducing the pressure upon said resistance medium, said pressure applying means being provided with a resilient cushion, adapted to automatically counteract in part the operation of the heat controlled pressure reducing means.

5. In an electrical current controller, a resistance unit having a positive temperature co-efiicient and containing a compressible resistance medium, whose electrical conductivity is increased when it is subjected to pressure, means for maintaining pressure upon said medium sufiicient to prevent separation of the conducting portions of said unit, and means for additionally compressing said medium to increase its conductivity.

6. An electrical current controller, comprising a resistance unit including a compressible resistance column of carbon disks and a thermally expansible device exposed to heat from said column and against which said column abuts, the other end of said device being connected with a fixed support,

in combination with a compressing member adapted to exert pressure upon said column, and resilient actuating donnections for vsaid compressing member.

7. An electrical current controller, including the combination of a resistance column composed of apertured disks, the resistance of which is diminished with increasing pressure, a thermally expansible rod connected with a fixed support and projecting through the disk apertures, an abutment on said rod at one end of said column of disks, and means for applying resilient pressure to the other end of said column of disks.

8. An electrical current controller, including the combination of a resistance column composed of a series of disks, the resistance of which is diminished with increasing pressure, an abutmentsupporting a thermally expansible member and extending longitudinally of said column of disks and exposed to heat therefrom, and means for applying resilient pressure to the other end of said column of disks, said pressure applying means being subject to manual control to increase or diminish the pressure upon said disks.

In tesfimony whereof I afiix my signature in the presence of two witnesses.

LYNDE BRADLEY.

Witnesses: LEVERETT C. WHEELER, 1. D. BREMER. 

